net/ncsi: Disable HWA mode when no channels are found

When there are no NCSI channels probed, HWA (Hardware Arbitration)
mode is enabled. It's not correct because HWA depends on the fact:
NCSI channels exist and all of them support HWA mode. This disables
HWA when no channels are probed.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>